The invention relates to a measuring method and equipment for determining the level, thickness and optical properties of an object to be measured with an optical measuring device.
In industrial processes there is a need to measure relief of surface of a product or its thickness as a measurement connected to the production process. Thereby, the product being the object of the measurement, for example, a film-like material moves by the measuring point. Examples of this kind of products include paper, rolled metal band or a plastic film. In manufacturing processes of all these products, the measuring of the relief of surface of the product can be performed, for example, mechanically by a sensor contacting the surface. A sensor contacting the surface can, however, damage the surface in a way that is not allowed by the end user.
Therefore, different electrical and optical measuring devices have been developed. In an optical measurement of surface, chromatic aberration can be used. In this kind of a measuring system, light is focused onto the surface to be measured through an optical element, the focal length of which depends in a known way on the wavelength of the light. The light reflected from the surface is collected either with the same optical element used for illumination or with another optical element to a detector. The wavelengths of the signal received by the detector are analysed and the spectral part that received the strongest signal is indicated. When it is known where the focus is in the measuring system, the location of the reflection point can be determined.